Analysis of physical influences of Solar flares on the lower part of the Earth\u27s ionosphere and its response to a total Solar eclipse

Magistrsko delo začnem z raziskavo medsebojne korelcije Wolfovega števila (merilo Sončeve aktivnosti) in števila Sončevih rentgenskih bliščev, ki so odgovorni za zemeljski atmosferski pojav nenadnih ionosferskih motenj (SID). To so izjemno močne gostote ionizacije v D sloju Zemljine ionosfere. Ko se blišč na Soncu zgodi, sunek močnega ultravijoličnega in rentgenskega sevanja zadane dnevno stran Zemlje. Visoko-energijsko sevanje absorbirajo delci v atmosferi, ki preko procesa foto ionizacije postanejo vzbujeni. Najnižjim slojem obsevane ionosfere (D in E sloj) se gostota elektronov nemudoma poveča. Ionosferske motnje ojačajo širjenje valov zelo nizkih frekvenc (VLF). S SID monitorjem, ki se nahaja na astronomskem geofizikalnem observatoriju Golovec v Ljubljani, detektiram blišče na Soncu tako, da spremljam moč radijskega signala oddaljenega VLF oddajnika, v odvisnosti od časa. Izmerjena motnja (SID) pove ali je zares prišlo do Sončevega blišča. Poleg tega obravnavam dnevne spremembe VLF signalov, kjer je glavni cilj izračun višine ter ocena efektivnega rekombinacijskega koeficienta in povprečne mase konstituentov odbojnega D sloja. V zadnjem delu naloge opazujem vpliv popolnega Sončevega mrka (21. avgust 2017) na spodnji sloj Zemljine ionosfere, z zmanjšanjem polnega vpadnega svetlobnega toka s Sonca. Ker se je stopnja ionoizacije v ionosferi (D sloj) zmanjšala, je efektivna odbojna višina narasla. Meritve sem opravil z VLF radijskim sprejemnikom LAVNet-Mex v Mexico Cityju, v Mehiki. V tem delu predstavljam podroben model mrka, ki temelji na enačbi fazne zakasnitve zaradi povečanja odbojne višine. Opisujem postopke modela in predstavljam pridobljeni profil faze in spremembe odbojne višine. Rezultati so skladni z rezultati prejšnjih mrkov (zemeljske in raketne meritve).The master\u27s thesis starts with the investigation of cross-correlation between Wolf\u27s number (Solar activity) and number of solar X-flares, which are responsible for a terrestrial atmospheric phoenomenon called a sudden ionospheric disturbance (SID). This is an abnormally high ionization density in the D layer of the Earth\u27s ionosphere. When a Solar flare occurs on the Sun a blast of intense ultraviolet and X-ray radiation hits the dayside of the Earth. This high energy radiation is absorbed by atmospheric particles, raising them to excited states and knocking electrons free in the process of photoionization. The low-altitude ionospheric layers (D and E layer) immediately increase in electron density over the entire dayside. The ionospheric disturbance enhances very low frequency (VLF) radio propagation. With an instrument called the SID monitor, located at Astronomical Geophysical Observatory on the Golovec hill in Ljubljana, I detect Solar flares by monitoring the signal strength of distant VLF transmitters over the course of time. The recorded SIDs indicate whether Solar flares have taken place. Furthermore I investigate diurnal variation of VLF signals, where I focus on calculation of the reflective height and an estimation of effective recombination coefficient and average mass of constituents at the reflecting D-layer. In the last part of the thesis I observe effects of the August 21, 2017 total solar eclipse caused on the lower part of the Earth\u27s ionosphere, by reducing the total incident flux from the Sun. As the rate of ionization in the ionosphere (D-region) was reduced, the effective reflection height increased. Measurements were done using the LAVNet-Mex VLF radio receiver in Mexico City, Mexico. In this work I present a detailed eclipse model which is based on the equation of the phase delay due to an increase in reflection height. I describe the steps of the model and present the obtained profile of the phase and reflection height variation. Results show a good agreement with the results from previous eclipses ground and rocket measurements